/home/brandsfa/www/vendor/mercadopago/dx-php/samples/payment/minimal/refund.php
<?php

    require_once dirname(__FILE__) . '/../../index.php';

    # Create a Payment
    require_once dirname(__FILE__) . '/create.php';

    # Refunding
    $refund = new MercadoPago\Refund();
    $refund->amount   = $payment->total_paid_amount;
    $refund->metadata = "A total refund";
    $refund->save();

    echo "Refund ID: " . $refund->id . "\n";
    echo "Payment Refunds: \n";
    var_dump($payment->refunds);

?>